The present invention is generally related to implantable devices and is more particularly directed to an implantable prosthesis having improved biocompatibility. Still more particularly, the present invention is directed to an implantable device having improved biocompatibility while providing systemic release of a therapeutic agent in tissue.
It should be appreciated that physiological compatibility and biocompatibility are common problems for both implants for providing a systemic, or local, release of the therapeutic agent and for prosthesis, i.e., implants, utilized for functional or cosmetic reasons, or both.
It should be appreciated that the term xe2x80x9cbiocompatiblexe2x80x9d in the present application relates to foreign object that can be left in a human or animal body for an extended or an indefinite period without causing any adverse physiological action.
The functional biocompatibility of an implant or device, is, of course, determined by the chemical and surface properties of the implant and its components. The general structure of a device, including mechanical strength, elasticity, flexibility, fatigue resistance, chemical inertness, impermeability to water, resistance to acid, etc., all contribute to biocompatibility which, of course, also depends upon the type of tissue into which the implant is to be inserted. Most importantly, the surface of the implant in contact with body tissues should also exhibit resistance to immunological attack, cell adhesion, pannus formation, etc.
Undesirable properties which can result from tissue interacting with the surface may significantly affect the efficiency of the implant and be counteractive to the intended use of the implant in certain medical devices, for example, sustained or controlled drug release devices.
The use of a sustained, or controlled release system has a well known advantage of providing an active agent at a relatively constant level of concentration in tissue. Sustained drug release systems have been utilized in a great number of applications including drug release into the vitreous for endophthalmitis and other vitreoretinal disorders with the use of antibiotics and a fungal agent, antineoplastic drugs and anti-inflammatory agents.
Unfortunately, in many instances, particularly where the implant is intended to remain in contact with tissue for extended periods of time, various problems associated with the physiological and chemical stability and compatibility with respect to various of the contacted tissues and biological fluids occurs. This is true even though the implant may function properly in its sustained or controlled release of the active agent.
For example, biomaterial such as a synthetic polymer, when contacted with blood, rapidly forms an adsorbed protein layer. Subsequently, conformational alterations and complexing of proteins which may occur which activate defense mechanisms such as coagulation, platelet adhesion, and aggregation, white cell adhesion, etc.
In eye tissue, an implant may cause superficial vascularization of the cornea with infiltration of granulation tissue. Biodegradable polymers may cause mild foreign body reactions which include inflammation in the vitreous.
Implanted biomaterials will cause a typical foreign body reaction with fibrinous membrane formation. A fibrinous membrane will surround and encapsulate the implant. Contraction of this fibrous capsule can range from transient pain to serious sequelae depending upon the location. Fibrinous infiltration of the vitreous with a prominent inflammatory response can lead to traction retinal detachment, disruption of the retinal pigmented epithelium or breakdown of the blood retinal barrier. Tissue and organ adhesions may develop as a result of the fibrinous inflammation. Intraocular implants can also cause cataract formation. Iris-ciliary body adhesions would seriously effect the homeostasis of ocular tension. Implants, being foreign objects, may cause acute and chronic inflammation. Tissue necrosis and scarring may result as well as neovascularization. Biopolymers may often be antigenic and elicit allergic or other adverse events. In the case of an implantable material in the vasculature or heart thrombus formation and embolus may occur.
In accordance with one embodiment of the present invention, an implantable device is provided for systemic, or local, release of a therapeutic agent in tissue. The device generally includes a therapeutic agent along with a carrier sized for insertion into tissue in which the systemic release of a therapeutic agent is desired, the carrier including means for providing sustained or controlled release of the therapeutic agent.
In addition, retinoid means, present in the carrier, is provided for improving biocompatibility of the device in the tissue.
As will be described in detail hereinafter, this hereinbefore unrecognized property of a retinoid substantially reduces or prevents undesirable attributes which can result from tissue interacting with the surface of the implantable device.
More particularly, in accordance with the present invention, the retinoid means may comprise a retinoid receptor agonist and the therapeutic agent, carrier, and retinoid means, may be homogeneous. This homogeneity provides for ease of manufacturing through the use of simple extrusion techniques or injection molding.
Specifically, in accordance with this embodiment of the present invention, the means for providing time release of the therapeutic agent may comprise a biodegradable polymer, such as, for example, a poly(lactic acid) and poly(lactide-co-glycolide).
More particularly, in accordance with one embodiment of the present invention, the carrier may be sized for implanting into a sclera and the retinoid receptor agonist may be a retinoid acid, for example, selected from the group of naturally occurring retinoids such as Vitamin A (retinol), Vitamin A aldehyde (retinal), Vitamin A acid (retinoic acid) and their synthetic and natural congeners. These would include but not be limited to the isomers all trans; 9-cis; 11-cis; 13-cis; 9, 11-dicis, and 11, 13-dicis as well as physiologically compatible ethers, esters, amides and salts thereof. The 7, 8-dihydro and 5, 6-dihydro congeners as well as etretinate are also acceptable for the invention.
Compounds that intrinsically or upon metabolism possess the physiologic properties of retinoids are also included within the scope of this invention. These would include synthetic and natural retinoid compounds having affinity to nuclear retinoic acid receptors (RARs) and retinoid X receptors (RXRs).
More particularly, the retinoid receptor agonist may be ethyl-6-[2-(4,4-dimethylthiochroman-6-yl)ethynyl]nicotinate, or 6-[2-(4,4-dimethylchroman-6-yl)ethynyl]nicotinic acid, or p-[(E)-2-(5,6,7,8-tetrahydro-, 5,5,8,8-tetramethyl-2-naphthyl)propenyl]-benzoic acid.
Corresponding to the device of the present invention, a method in accordance with the present invention for improving biocompatibility of an implant in tissue generally includes the steps of providing a therapeutic agent, providing a carrier sized for insertion into tissue in which release of the therapeutic agent is desired, incorporating a therapeutic agent into a carrier in a manner enabling sustained or controlled release of the therapeutic agent and incorporating a retinoid into the carrier in an amount effective for improving biocompatibility of the carrier in the tissue.
Many conditions and diseases are treatable with stents, catheters, cannulae and other devices inserted into the esophagus, trachea, colon, biliary tract, urinary tract and other locations in the body, or with orthopedic devices, implants, or replacements. It would be desirable to develop devices and methods for reliably delivering suitable agents, drugs or bioactive materials directly into a body portion during or following a medical procedure, so as to treat or prevent such conditions and diseases, for example, to prevent abrupt closure and/or restenosis of a body portion such as a passage, lumen or blood vessel.
As a particular example, it would be desirable to have devices and methods which can deliver an antithrombic or other medication to the region of a blood vessel which has been treated by PTA, or by another interventional technique such as atherectomy, laser abllation, or the like. It would also be desirable that such devices would deliver their agents over both the short term (that is, the initial hours and days after treatment) and the long term (the weeks and months after treatment). It would also be desirable to provide precise control over the delivery rate fro the agents, drugs or bioactive materials, and to limit systemic exposure to them. This would be particularly advantageous in therapies involving the delivery of a chemotherapeutic agent to a particular organ or site through an intravenous catheter (which itself has the advantage of reducing the amount of agent needed for successful treatment), by preventing stenosis both along the catheter and at the catheter tip. A wide variety of other therapies could be similarly improved.
Another embodiment of the present invention includes an implantable device, specifically a surgically implantable prosthesis in combination with retinoid means for improving the biocompatibility of the prosthesis. More specifically, the retinoid means may be present in the form of a film on the prosthesis or, alternatively, bonded to a surface of the prosthesis.
Other implants to be considered as part of the present invention include biocompatible stents such as described in U.S. Pat. Nos. 5,342,348 and 5,554,381, biocompatible bone pins such-as described in U.S. Pat. No. 4,851,005, biodegradable/biodegradable joint prosthesis such as described in U.S. Pat. No. 6,007,580, biodegradable birth control devices such as described in U.S. Pat. No. 5,733,565, biodegradable implants for treatment of prostate cancer or any biodegradable drug delivery system.
All of the hereinabove referenced patents are to be incorporated herewith, including all drawings and specifications, by this specific references thereto.
As hereinabove noted, the retinoid means may comprise a retinoid selected from the group of naturally occurring retinoids such as Vitamin A (retinol), Vitamin A aldehyde (retinal), Vitamin A acid (retinoic acid) and their synthetic and natural congeners. These would include but not be limited to the isomers all trans; 9-cis; 11-cis; 13-cis; 9, 11-dicis, and 11, 13-dicis as well as physiologically compatible ethers, esters, amides and salts thereof. The 7, 8-dihydro and 5,6-dihydro congeners as well as etretinate are also acceptable for the invention.
Compounds that intrinsically or upon metabolism possess the physiologic properties of retinoids are also included within the scope of this invention. These would include synthetic and natural retinoid compounds having affinity to nuclear retinoic acid receptors (RARs) and retinoid X receptors (RXRs)
Importantly, the present invention encompasses a method for improving biocompatibility of a surgically implantable prosthesis with the method comprising the step of combining a retinoid with the prosthesis. More particularly, the step may include disposing a film of retinoid on the prosthesis or, embedding retinoid, to the surface of the prosthesis. The retinoid may comprise a retinoid, as hereinabove noted, and be selected from the group of naturally occurring retinoids such as Vitamin A (retinol), vitamin A aldehyde (retinal), Vitamin A acid (retinoic acid) and their synthetic and natural congeners. These would include but not be limited to the isomers all trans; 9-cis; 11-cis; 13-cis; 9,11-dicis, and 11,13-dicis as well as physiologically compatible ethers, esters, amides and salts thereof. The 7, 8-dihydro and 5,6-dihydro congeners as well as etretinate are also acceptable for the invention.
Compounds that intrinsically or upon metabolism possess the physiologic properties of retinoids are also included within the scope of this invention. These would include synthetic and natural retinoid compounds having affinity to nuclear retinoic acid receptors (RARs) and retinoid X receptors (RXRs).